I live in a very old house (1850's) with a septic system and some anomalies. After a recent problem with a busted pipe outside causing a cabbagey smell, the septic guys discovered that there was a whole house trap outside the house (as well as a Y where the rest of the house's plumbing met the main septic line). While they replaced both of those lines (unhappy that the Y was outside but unable to change that for the moment...) they also closed the trap and replaced with straight pipe. Now the cabbage smell is gone but we have sewer gases coming out into the bathrooms whenever we use a fixture. Clearly the trap was keeping these gases from entering the house. The question is, do we have a trap put back in the yard with a vent and a cleanout, or start busting into walls to check the indoor venting system, and put a roof vent in (there is none)? Thanks for any advice - I don't know anything so I am eager to understand. We would like to do this right but avoid unnecessary work.

Normally, I would NEVER suggest installing a "whole house trap". Therefore, the question is, "Where are the odors coming from"? If there are NO vents out the roof, then siphonage of the traps is the prime suspect, but also, without a vent and with a house trap, nothing should have drained, unless the traps were being siphoned. You want to correct the problem, not just the symptoms.

at very least you need a vent stack thru the roof.
as for the smell... it could be improper venting or lack of a p-trap under a fixture or it could even be a cracked cast iron pipe somewhere ???
each scenario would require a different fix.

Thanks aj & packy. The smell is really coming from behind the wall where the plumbing is, in both bathrooms - one above the other. Everything seems to have traps except perhaps a downstairs bathroom sink (will look into that too) but the worst smell seems to be upstairs. Time perhaps to take a look behind that wall to see if there are any pipes in need of replacement or any old vents, and put in a roof vent. Any other thoughts appreciated.



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If someone just cut a vent off, in a wall or in the attic, instead or running it through the roof, that would be all you need to get the odors. They WOULD come in through the walls.

thanks hj. will let you know what we find...



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I think a lot of older houses had those whole house traps back in the day, it was probably seen as a common-sense thing to do to protect the entire house from sewer gases and maybe sewer rodents, even if fixtures also had their individual traps. Nowadays just about everyone recommends removing them to eliminate a potential source of blockages. But in your case the whole house trap was probably preventing an odor problem caused by something else awry that was done in the plumbing that depended on the whole house trap being there. When we bought our house there was a whole house trap, we found out that the washing machine standpipe had no trap, it was connected straight to the main drain pipe. So without the whole house trap we had sewer odors in laundry room until the standpipe was redone.

As you said, you will need to inspect the pipes and find out where the odor is leaking. A plumber can do a "smoke" test where they cap off the roof plumbing vents and inject smoke into the drain pipes, then look for smoke leaking out of the problem area somewhere in the house.



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indeed, i believe that the whole house trap was there for a reason - the problem very clearly started when it was taken out... we do think that all everything has a trap though. it's confusing.

This has been discussed before, whole house traps are required in NY: [www.plbg.com]

If required in NY why did the NY plumbers remove their whole house trap?

BEcause it is a stupid requirement imposed by someone who does not know what he is doing.

Required maybe in NYC, but not in NY state outside of the city? Since the OP is on a septic system they are likely outside NYC. Or the guys doing the work thought they were doing them a favor by removing it since it so often causes trouble. Plumbing supply places are still selling whole house traps, so people are still installing them on new-build homes or as a replacement.



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Required in NYC and Long Island. OP may indeed be upstate or if he has a cesspool he may be on LI. I'm not a plumber so I'm not qualified to pass judgement on whether these things are good or bad. I have had 3 houses with these things and they have never been a source of clogs.

We are in Catskill, north of NYC. Not sure if it's required or not. I have read the other threads where some people are for whole house traps and many more are vehemently against them. The septic guy thinks it is "plumbing 101" to remove the whole house trap, but two local plumbers have come to take a look at our house and both say the first step should be to re-install a trap, vent it (it was not vented), maybe put a cleanout (it is about 3 inches underground so may not be necessary), and then install a roof vent and try to suss out any other problems. It's an old farmhouse and there are a many anomalies in the current plumbing. we did have a smoke test for the initial problem (before main line and other external line were replaced and trap taken out) and at that point the only smoke we saw was pouring in foundation, but that has been fixed by replacing the outside pipes. again the smell started only after closing the whole house trap.

If you're ok with having a new whole house trap installed then I'd say do it. It should deal with the sewer odor problem and since you are aware of the negatives of having a whole house drain you can deal with any clogs in it that may happen. If you do this I'd be sure to follow the recommendations about having it vented and having cleanouts for it easily available. If it ever does clog it will be on a weekend when you have house guests, so make unclogging it as easy as you can.

Keep in mind that the indoor sewer odor you have is real and it is coming from somewhere, that means there is potentially an opening or leak someplace in your household drainage plumbing and it would be advisable to get it corrected. The whole house trap won't correct that, it just makes it livable. The smoke test did not show any drain line problems that accounted for the sewer odor? Did someone inspect the attic as suggested earlier and look for a broken or disconnected plumbing vent pipe? What's this about getting a roof vent installed, did they find something that needs attention?



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This is sound advice - thank you.

The smoke test only showed the problem in the pipes outside where smoke was pouring in through our foundation, no smoke in the house. But perhaps that problem there was so bad smoke didn't make it through the whole system...

There are no pipes/vents in the attic - which is why we thought we should add the roof vent... Looking behind walls today to see if we can understand more of what's going on.



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When you say you are considering adding a roof vent does that mean there are no vent pipes coming thru the roof at this time? If not, how are the plumbing drain lines in the house vented? The upper end of a plumbing vent pipe is open so the odor and sewer gas can escape, so obviously it needs to be outside the home.

There is no vent going to the roof - or to the outside at all other than one of the bathroom fans - nothing that we can find.

well, that could be what's going on with the sewer odor you have. As you know a vent is used to carry those odors out of the drain pipes in your home to the outside world where they diffuse/dilute and don't cause a problem. If indeed there are not any drain vents then the whole house trap was very important for blocking sewer vapors from entering the home drain piping. The vent also lets air come into the drain pipe when a large slug of water runs down the drain, like when you flush a toilet or pull the stopper after a bath. This lets the water go down the drain better without any vacuum effect pulling on the drains traps and possibly sucking the water out of the trap. With modern plumbing every fixture has a trap and every trap is vented, so ideally you'd get your house plumbing updated with this in mind, balancing cost with benefit.

Talk to your plumber about getting a plumbing vent added and ask him if there could be any "hidden" vents somewhere in the house. If he has been plumbing in that area for many years he will know how houses like yours are plumbed and can make the best recommendation for your particular setup. If you have the whole house trap installed and vented that will help keep sewer odors from coming in from the street sewer line to your drain pipes inside your house. But your home's bathroom and laundry drain pipes will have their own odors that need to be vented outside. Ask him if you do add a rooftop vent (or two) in the right places would that mean you'd no longer need the whole house trap? If so, that could save part of your cost. He could add the rooftop vent, then see how well it does or does not take care of the problem, then add the whole house trap if needed.



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Just an update... we decided to wait on having whole house trap put back in when we discovered that we had an old rusty vent pipe going to nowhere. Put in an intake to see if a new vent would fix the problem, but problem still there. So we are waiting now to put vent in and replace some of the older pipes beneath upstairs bathroom. Hoping that fixes it, and still wondering if we should have the septic guys back to replace the whole house trap... been living with methane for too long now!